River Seine's banks not straight (5)

I believe the answer is:

false

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'river seine's banks not straight' is the definition.
I can't judge whether this defines the answer.

'river seine's banks' is the wordplay.
'river' becomes 'fal' (Cornish river).
'banks' suggests removing the centre (the banks are the edges of the word).
'seine' with its centre taken out is 'se'.
'fal'+'se'='FALSE'

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(Other definitions for false that I've seen before include "Erroneous" , "Invalid; untrue" , "Wrong" , "Incorrect" , "Bogus" .)

I've seen this clue in The Guardian.

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